The invention is directed toward machines that consist in an injection mold with a mandrel on which the plastic material in paste consistency is deposited, the mandrel being released from the injection mold and inserted into a shaping mold into which compressed air is sent so that the plastic material is applied on the internal surface of this mold.
Generally, these machines consist in series of injection molds and series of shaping molds, and are constructed in such a manner that the shaping is done at the time of injection, and vice versa.
The passageway provided for the compressed air at the time of shaping must be very small in size, and it has been found that regardless of the care taken the air could always carry impurities that can obstruct said passageway. In this case, cleaning that is very complex and lengthy and immobilizing the machine for a lengthy period of time must be done.
What is desired therefore is a mandrel assembly having means for closing the compressed air passageways during the injection molding process, yet allowing the passageways to open during the shaping mold process.